Known cryogenic refrigerators will be explained with reference to a Joule-Thomson refrigerator. The Joule-Thomson refrigerator described in Japanese Patent Laid-Open Publication No. H10-26428and U.S. Pat. No. 4,766,741 uses the Joule-Thomson effect for attaining the refrigeration performance. With the Joule-Thomson effect, the temperature declines as the pressure of the high pressure gas declines. The Joule-Thomson refrigerator includes a high pressure gas source, a heat exchanger, and a Joule-Thomson valve. The high pressured gas of the high pressure has source is introduced to the heat exchanger to be refrigerated with the return of the low pressured gas at the heat exchanger. Further, the high pressured gas generates enthalpy expansion to have the low pressure through the Joule-Thomson valve, or the like, to decline the temperature of the refrigerant, which provides the refrigeration performance.
Generally, a 4K refrigerator for obtaining the refrigeration at approximate to 4K includes a Joule-Thomson refrigerator including a Joule-Thomson circuit, a two-stepped pulse tube refrigerator for pre-cooling, and a compressor unit for supplying the high pressure gas. This is the effective method for achieving the temperature at 4K by helium gas. The 4K refrigerators are mainly used for refrigerating MR1, SQUID, and other superconductive device, or the like.
The refrigerator including the Joule-Thomson circuit and the two-stepped pulse tube refrigerator for the pre-cooling mainly include three parts including the compressor portion, the Joule-Thomson circuit, and the two-stepped pulse tube refrigerator.
The cryogenic refrigerator further advantageous for obtaining the cryogenic temperature is to be developed.
A need thus exists for a cryogenic refrigerator which is advantageous for attaining the cryogenic temperature and advantageous for the liquefaction of the refrigerant.